Heat activated air shutter for fireplace and related methods

ABSTRACT

The present invention is directed to a heating unit, such as a fireplace, including an interior housing forming a combustion chamber. The housing includes a top wall, a rear wall and side walls defining an exterior housing about the combustion chamber. A burner assembly is positioned to provide combustion to the combustion chamber and a heat activated shutter is provided in communication with the burner assembly for controlling flow of air into the burner assembly so as to produce a yellow flame within the unit in a generally instantaneous time period.

This application claims benefit of U.S. Provisional Application No.60/780,290, filed Mar. 8, 2006.

FIELD OF THE INVENTION

The present invention relates generally to fireplaces and similardevices. In particular, the present invention relates to an apparatusand methods by which the airflow to a burner of a fireplace or otherheating/lighting unit may be regulated. More particularly, with respectto embodiments of the apparatus, the present invention includes an airshutter assembly that is generally automatically responsive to heat forcontrolling primary airflow to a main burner and/or a secondary burnerto a gas fireplace or similar heating/lighting unit.

BACKGROUND OF THE INVENTION

Fireplaces are desirable features in the home. However, devices thatburn non-solid materials, such as gas, or that produce heat electricallyhave gradually replaced traditional wood or other solid fuel-burningfireplaces. Like, wood, the combustion of gas does provide real flamesand heat, but requires a careful mixing of gas and air for optimalperformance and a realistic flame. This aspect of the gas fireplace, andsimilar appliances, typically involves the delivery of air forcombustion to an arrangement or device where the air is mixed withgaseous fuel, e.g., natural gas and propane (“gas”). Clearly, it isadvantageous that the air and gas are mixed at a ratio for propercombustion. Then, the mixed air and gas are delivered to a burner, andultimately provided to a combustion chamber of the fireplace. In someinstances, the mixing of air and gas is accomplished in the actualburner itself.

Multiple such arrangements have been created that are passive in nature,such as manifolds of a given size and shape with orifices designed todeliver a fixed ratio of air and gas for combustion. This ratio istypically optimized at a steady state, heated operating condition. It iswell known that what is termed the “steady state” operation of a gasfireplace is achieved after the unit has had an opportunity of burn for30 minutes or more. Some manifolds, ducts, inlet passages, air passagesand the like are routed through the fireplace to preheat the combustionair and increase the efficiency of the fireplace. One example of such adevice is illustrated in U.S. Pat. No. 6,295,981, which is incorporatedin its entirety by reference.

As a fireplace, or similar type of unit transitions from an initial orcold start condition to ultimately the “steady state” condition ofcombustion it has been observed that the change in efficiency of thecombustion and an increase in the heat generated causes a change in theproperties of the flames produced. Namely, the flames tend to be blue atthe onset of combustion when the unit components and intake,gases aregenerally at room temperature or, given that heating units may not beused only in interior locations, other ambient temperature. The flamesgradually transition to a more desirable yellow color as heat increasesand combustion becomes more complete. Since the air/gas ratio of theknown unit is typically preset for correct burning at a heated, steadystate condition in conventional gas fireplace units, a unit may operateunder less than ideal combustion conditions from the initial cold startand for a long initial period of time thereafter. Very little yellowflame is observable during this period.

The generation of a blue flame is symptomatic of a “pre-steady state”condition, also termed “start-up” condition. Separate and apart fromwhat is occurring inside the heating unit, a predominantly blue flame isdisadvantaged in a sales environment. However, consumers do notnecessarily find a heating unit that is generating a blue flame to bedesirable. Consumers wish to see a unit with a yellow flame since theycan more easily envision how the unit will look in their home when fullyoperated. Consumers that ask to see the operation of various heatingunits made by various manufacturers at the point of purchase may likelymake their purchasing decision based on which one produces the yellowflame quicker.

Whereas many gas/air mixing schemes are simply designed and set for asteady state condition, i.e., at operating temperature at equilibrium,some fireplaces provide a mechanism for adjusting the air/gas mixture.However, if improperly adjusted or malfunctioning, these types ofschemes can be unreliable, can produce improper air/gas mixtures, andcan cause a buildup of soot or unburned carbon deposits or a dangerouscondition.

There is a demand therefore, for a simple, reliable, and cost-effectiveway of producing desirable combustion and aesthetic flame conditions ofa fireplace unit or the like in a generally instantaneous manner thatis, without the wait for the known transition from an initial cold startcondition to the fully “steady state” condition. The present inventionsatisfies that demand.

SUMMARY OF THE INVENTION

The present invention has an objective of providing a desirable mixtureof combustion air to a fireplace as the fireplace transitions from acold start condition to a steady state, heated condition. One example ofa fireplace that would be a suitable candidate for the invention is amodel “DV360” fireplace manufactured by CFM Corporation. It will beunderstood that the invention contemplates any suitable gas fireplace orlike device. More specifically, the invention is directed to anautomatic, heat activated air shutter assembly for moderating the amountof air entering a burner assembly of a fireplace. The air shutter collarassembly is opened and closed by one or more bi-metal coils attached tothe shutter in such a fashion so that an increasing amount of air ispermitted to enter the burner assembly as the heat acting on the coil(s)increases.

The fireplace may include a housing, which may take any suitable form asneeded or desired and may be in the form of an enclosure or framework,sized and shaped according to a number of considerations. Examples ofthese considerations include budget, space, aesthetic, mechanical,safety, and other design and operating considerations. Generally, thehousing is an enclosure or structure in which or to which mechanisms andcomponents are enclosed or attached. The housing is also that which isattached at an installation location. The housing or box may bemanufactured from a wide variety of materials, including plastic resinsuitable for the application, sheet metal, burner tube material or anyother material known to those skilled in the art.

One embodiment of the housing includes a top panel, a bottom panel, aback panel and opposing side panels. The two opposing side panels arefurther optional depending on the application. The housing of thisembodiment is sized and shaped to accommodate a fire display boxpositioned therein. The fire display box is designed to present to aviewer the impression of a working, more traditional fireplace. The firedisplay box may be open to the front for viewing purposes and mayoptionally be provided with a fixed or movable front panel or panels,which may be at least in part transparent, translucent or opaque. Forpurposes of this application, the front of the fireplace unit is thatside of the unit through which the interior of the unit is at leastpartially viewable. It should be understood that the exemplary unit usedto describe the invention herein will be similar to a conventionalfireplace with a single front panel, through which the interior of thefireplace may be viewed. However, the invention also contemplates a“dual-front” or “see-through” unit or other suitable units in which itis desirable to automatically control the flame appearance.

A fire display box is positioned in the housing. For purposes of thisapplication, the term “fire display box” will broadly signify the areasimilar to the portion or area found in a fuel-burning fireplace inwhich combustion takes place and from which the fire that is producedthereby may be viewed. Traditionally, this area is known as a “firebox,”“box,” or “fireplace.”

Combustion takes place in or near the firebox by way of a burner, whichis supplied with air and gas and preferably some form of pilot light orignition device with which to ignite the air and gas mixture. A shutteris attached on or near the burner or in the intake air pathway tocontrol the flow of intake air into the burner. The shutter includes oneor more bi-metal coils attached thereto. When the burner is first lit,the burner assembly, shutter and coils are at ambient temperature andthe shutter is in a closed condition. This condition permits a reducedamount of intake air to enter the burner housing. The burner, shutterand coils gradually warm to a heated condition and, in response, thecoils function to open the shutter to provide an increased amount ofintake air over the time the burner transitions from an initial ambienttemperature to a steady state heated condition.

It has been found that the desired, yellow appearance of the flame maybe achieved in an instantaneous fashion by use of the bi-metal coil andshutter assembly according to embodiments of the invention.“Instantaneous” for purposes of this invention is considered about 1-5minutes, which is a significant improvement over the prior art systemswhich take much longer to produce the desired yellow flame.

The invention provides, in one embodiment for example, a gas heatingunit, including a combustion chamber. A burner housing assembly ispositioned in the heating unit to provide combustion to the combustionchamber, wherein the burner housing assembly includes a burner housingand a gas and air mixing assembly in communication with said burnerhousing. The gas and air mixing assembly functions to mix gas and air toprovide a yellow appearing flame instantaneously after initiation ofcombustion.

Another aspect of the invention provides a gas and air mixing assemblyautomatically responsive to changes in temperature to maintain saidyellow appearing flame over time. Yet another embodiment of theinvention provides a gas heating unit, including a combustion chamberand a burner housing assembly positioned to provide combustion to saidcombustion chamber, wherein the burner housing assembly includes aburner housing and a gas and air mixing assembly in communication withthe burner housing. The gas and air mixing assembly includes a mixingtube assembly. The mixing tube assembly includes a mixing tube having atleast one air opening formed at an outer end thereof and a shuttercollar assembly sized, shaped and positioned to seal with the at leastone air opening of the mixing tube. The shutter collar assembly isattached to a bi-metal coil spring. The bi-metal coil spring isresponsive to changes in temperature to withdraw the shutter collarassembly from the at least one air opening in response to an increase oftemperature from an ambient temperature and permitting air to enter theat least one air opening.

Yet another embodiment of the invention provides a method of controllingthe color of a flame in a heating unit, including the steps of supplyinga burner housing of the heating unit with a flow of gaseous fuel,sensing an initial start up condition of the heating unit, limiting theamount of air flow into the burner housing of the heating unit inresponse to the sensing of the initial start up condition to generate aninstantaneous yellow appearing flame upon combustion, sensing anincrease of temperature relative to the initial start up condition, andincreasing air flow into the burner housing in response to the sensingan increase in temperature to maintain the color of the flame.

These and other advantages, as well as the invention itself, will becomeapparent in the details of construction and operation as more fullydescribed and claimed below. Moreover, it should be appreciated thatseveral aspects of the invention can be used in other applications whereaesthetically pleasing flames would be desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a gas fireplace suitable for use with theburner assembly of the invention;

FIG. 2 shows a perspective view of an assembled burner housing assemblymade in accordance with one embodiment of the present invention;

FIG. 3 shows an expanded perspective view of the burner housing assemblyof FIG. 2;

FIG. 4 shows an exploded view of a dual spring assembly, shutter collarassembly and mixing tube assembly according to an embodiment of theinvention;

FIG. 5 shows a perspective view of the assembly of FIG. 4 assembled;

FIG. 6 shows a partial top view of the assembly of FIG. 5;

FIG. 7 shows an end view of the assembly of FIG. 4;

FIG. 8 shows a side view of the mixing tube assembly in an assembledcondition;

FIG. 9 shows a perspective view of a mixing tube assembly in an expandedcondition;

FIG. 10 shows a perspective view of a mixing tube;

FIG. 11 shows an end view of mixing tube;

FIG. 12 shows a first side view of a mixing tube;

FIG. 13 shows a second side view of a mixing tube rotated 90 degrees;

FIG. 14 shows an end view of a spring plate;

FIG. 15 shows a perspective view of a spring plate;

FIG. 16 shows a side view of a spring plate;

FIG. 17 shows a side view of a tube cap;

FIG. 18 shows the tube cap of FIG. 17 in an end view;

FIG. 19 shows an expanded perspective view of another embodiment of amixing tube assembly and bimetal coil spring assembly;

FIG. 20 shows a side view of a spring bar;

FIG. 21 shows an end view of a spring bar;

FIG. 22 shows a perspective view of a spring bar;

FIG. 23 shows a top view of bimetal coil spring;

FIG. 24 shows a side view of the bimetal coil spring of FIG. 23; and

FIG. 25 shows an expanded view of the shutter collar assembly.

DETAILED DESCRIPTION OF A PRESENTLY PREFERRED EMBODIMENT

The present invention will now be described in detail with reference tocertain embodiments thereof as illustrated in the accompanying drawings.In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention andhow it may be applied to a gas fireplace. It will be apparent, however,to one skilled in the art, that the present invention may be practicedwithout some or all of these specific details. In other instances,well-known process steps and/or structures have not been described indetail to prevent unnecessarily obscuring the present invention.

FIG. 1 illustrates a gas-fueled heating unit, which in a preferredembodiment is a fireplace in accordance with one embodiment of thepresent invention. Referring to FIG. 1, a gas heating unit 60 includes acombustion chamber 61 with sidewalls (not shown), a rear wall 66 and topand bottom walls 63 and 65. Simulated logs, e.g., ceramic gas logs 68are arranged in a conventional manner over a burner housing assembly 100according to an embodiment of the invention. A glass front door (notshown) closes the combustion chamber 61 and provides visual accessthereto. While the invention will be described by reference to a unithaving a single glass front door, the unit may also be what is termed a“dual-front” or “see-through” unit.

Surrounding the combustion chamber 61 is a unit housing or fireplacehousing 67. Air circulation pathways are formed within the fireplacehousing 67 in a conventional manner. One such pathway allows room air tobe brought in from the bottom front of the fireplace housing and beneaththe combustion chamber 61 (arrows 72). The room air is then directedalong the rear of the combustion chamber 61 (arrows 73). Finally, theroom air is directed along the top of the combustion chamber 61 (arrows74) and back into the room. At this point, the room air has been heateddue to the placement of the pathway air proximate to the heatedcombustion chamber 61.

In another pathway, combustion air (i.e., air entering the combustionchamber 61) is brought in from the exterior of the building through aconcentric flue pipe assembly common to this type of fireplace. As willbe described below, the combustion air can enter from one of twoavailable ports. Once within the fireplace housing 67, the combustionair travels a pathway immediately outboard of the room air pathways.That is, the inboard side of the combustion air pathway includes thewall structure forming the outboard side of the room air pathway. Thisplacement also aids in the heating of the room air contained within theroom air pathways. Combustion air travels downward through the rear ofthe heating unit 60 (arrows 75), then into the combustion chamber 61(arrow 76) through combustion chamber air inlets 78 formed in a bottomportion of the rear wall 66. The fireplace housing 67 has exteriorsidewalls (not shown), top wall 82, a bottom wall 83 and a rear wall 84.

Disposed within the combustion chamber 61 is a burner housing assembly100 according to an embodiment of the invention. The burner housingassembly 100 includes a heat-activated mechanism 102 according to anembodiment of the invention. The heat-activated mechanism 102 regulatesthe mixing of gas and air entering the burner housing assembly 100 inresponse to changes in temperature by changing the mixture of gas andair in a manner that will be described in greater detail below.

Ignition of the gas and air mixed by the heat-activated mechanism 102produces a yellow flame or flames 200 in an instantaneous fashion (whichagain for purposes of this application means in about 1-5 minutes afterinitial ignition) and not in the 30 or more minutes that the prior arttakes to produce a yellow flame. The mechanism 102 maintains theappearance of the flames 200 generally from a start up condition of theunit through a steady state condition.

Described herein is a fireplace assembly with a heat-activatedmechanism, which provides for a predetermined ratio of air and gas at acold start up condition and transitions to a heated and steady statecondition in response to changes in temperature, experienced by themechanism. While the above-described assembly is intended to be usedwith a fireplace, it is to be realized that the described arrangementaccording to the embodiments of the invention could be incorporated inother types of units, such as for example, direct vent, natural vent andvent-less fireplace systems and even gas operated units which are notfireplaces.

FIG. 2 shows an assembled burner housing assembly 100 according to anembodiment of the invention that includes a burner housing 101 and anassembled gas and air mixing assembly 102. The burner housing assembly100 includes a number of associated or attached components, the detailsof which are provided in FIG. 3 and the following drawings. Generally,the burner housing assembly 100 includes a burner housing 101, which hasa rectangular shape, within which gaseous fuel and air are mixed atleast in part through the functioning of the gas and air mixing assembly102. The burner housing 101 may be fastened together by welding, forexample. Other suitable shapes of the housing are contemplated.

Turning to FIG. 3, the burner housing 101 is provided with a portloading channel 104, which fits atop the burner housing and closes theburner housing. Preferably, the port loading channel 104 is providedwith a sealant, (not shown) to effect a seal with burner housing 101.Port loading channel 104 includes a plurality of port loading channelopenings 106 formed therethrough for gas and air to leave the burnerhousing in a pattern which may be designed and intended to producedesired flame patterns.

A port loading channel gasket 108 is positioned atop port loadingchannel 104. One or more ceramic tile 110 is positioned adjacent or atopthe port loading channel gasket 108 at least in part to protect theburner housing assembly 100 from direct exposure to heat from flames.The one or more ceramic tile 110 is flanked by one or more burner tilegasket 112. The one or more ceramic tile 110 is held in place by firstand second ceramic tile mounting angles 114, which fasten to the burnerhousing 101 by conventional fasteners 116, such as screws. A securingbracket 118 attaches to the burner housing 101 and includes a pair oflog spacer brackets 120, which log spacer brackets overlay ceramic tiles110 when fastened to the securing bracket.

The burner housing assembly 100 may include other devices for supportingan artificial log set (not shown) above the burner housing assembly. Forexample, a front log support bracket 122 may be mounted to the burnerhousing 101 over the ceramic tile mounting angles 114.

The burner housing 101 includes a burner housing opening 126. The gasand air mixing assembly 102 is disposed in the burner housing opening126. A spring plate gasket 128 is interposed between the burner housing101 and gas and air mixing assembly 102 to create a seal with the burnerhousing opening 126. Details of each of the above assemblies andelements of the burner housing assembly 100 are provided hereinbelow.

FIGS. 4-7 show the air and gas mixing assembly 102 in detail. The airand gas mixing assembly 102 includes a mixing tube assembly 130, whichis further detailed in FIGS. 8 and 9. The mixing tube assembly 130includes mixing tube 132, which is an elongated cylinder shape. Upperand lower air openings 134, 136 are formed at an outer end 138 of themixing tube 132. An annular or washer shaped tube cap 140 is positionedat the outer end 138 of the mixing tube 132.

A shutter collar assembly 142 positioned over the upper and lower airopenings 134, 136 is sized and shaped to close over the upper and lowerair openings 134, 136. At ambient air temperatures, the shutter collarassembly 142 is held closely against the mixing tube 132 so as to closeoff the upper and lower air openings 134, 136. The shutter collarassembly 142 is held in the closed condition at ambient temperatures byrespective upper and lower bi-metal coil springs 144, 146, which areconfigured to bias the shutter collar assembly 142 in the depictedposition. The shutter collar assembly 142, which is disposed on theupper air opening 134, may be considered a first shutter collarsubassembly 142 a and the shutter collar assembly, which is disposedover the lower air opening 136, may be considered a second shuttercollar subassembly 142 b.

Each of the upper and lower bi-metal coil springs 144, 146 are fastenedto a spring bar 148, which in turn is fastened to a spring plate 150.Spring plate 150 has an opening 152 which is sized and shaped to receivethe mixing tube 132.

It can be seen, especially in FIG. 7, that the bi-metal springs on 144,146 hold the shutter collar assembly closely around the periphery of themixing tube 132 at the outer end 138 thereof (see FIG. 4). In this way,air is not drawn into the mixing tube 132 during operation because theshutter collar assembly 142 closes over the upper air are opening 134and the lower air openings 136. The bi-metal coil springs 144, 146 areconstructed and oriented in such a fashion to uncoil and pull theshutter collar assembly 142 away from the mixing tube 132 thus exposingthe upper air opening 134 and the lower air opening 136, which permitsair to enter interior of the mixing tube 132, mix with gaseous fuel andenter the burner housing 101 (see FIG. 3, for example). The embodimentof the gas and air mixing assembly 102 shown in FIGS. 4-7 is intendedfor use with natural gas, but may be adapted for use with LP gas, as inknown in the art and is also shown below with reference to FIG. 19.

FIGS. 8 and 9 show the mixing tube assembly 130. The mixing tubeassembly 130 includes a cylindrical mixing tube 132. The mixing tube 132is also shown in FIGS. 10-13. Referring then to FIGS. 8-13, at the outerend 138 of the mixing tube 132 are formed a pair of cutaway sections,which when tube cap 140 is attached to the outer end of the mixing tubecause the formation of openings 134, 136. The tube cap 140 has a washeror annular shape with a cap opening 141 centrally located therethrough.Spring plate 150 is generally and L-shaped bracket having a plateopening 152, which is sized to receive the mixing tube 132. A springplate 150 is positioned close to the outer and 138 of the mixing tube132. The mixing tube assembly 132 may be assembled by welding, forexample.

FIGS. 14-16 show spring plate 150 in detail. Spring plate 150 has aspring plate tube section 158 that includes plate opening 152. A springplate bend 156 separates the spring plate tube section 158 from a springplate spring section 160 at an angle of about 90 degrees. The springplate spring section 160 includes a pair of spaced spring receiving tabs154.

FIGS. 17 and FIG. 18 show tube cap 140, which has a flat washer shapeand a centrally located cap opening 141. Tube cap 140 is attached to theouter end 138 of mixing tube 132 (see FIG. 8, for example). Theattachment may be accomplished in any suitable fashion, for example bywelding.

FIG. 19 shows an embodiment of a mixing tube assembly and a partialshutter collar assembly in detail and usable with LP gas (propane). Themixing tube assembly 230 includes mixing tube 132, which is an elongatedcylinder shape. Upper and lower air openings 134, 136 are formed at anouter end 138 of the mixing tube 132. An annular or washer shaped tubecap 240 is positioned at the outer end 138 of the mixing tube 132. Amanually adjustable choke sleeve 162 is provided on the mixing tube 132and has the general shape of a flattened ring with a pair of cutouts 164corresponding in shape and size to the upper and lower air openings 134,136. The choke sleeve 162 is slidably and rotatably positioned on themixing tube 132 and over the upper and lower air openings 134, 136 andwhen rotated can be used to cover or uncover the upper and lower airopenings and thus adjust how much of the openings are exposed. A setscrew 166 is provided in a slot 168 of the choke sleeve 162 to fix thechoke sleeve in place, preferably after adjustment for a desiredair/fuel ratio.

Each of the upper and lower bi-metal coil springs 144, 146 are fastenedto a spring bar 148, which in turn is fastened to a spring plate 150.Spring plate 150 has an opening 152 which is sized and shaped to receivethe mixing tube 132. The free ends 180 of the bi-metal coil springs 144,146 occlude the upper and lower air openings 134, 136 when in an initialstart-up condition (i.e., ambient temperature). As the temperatureincreases, the bi-metal coil springs 144, 146 unwind and draw away fromthe upper and lower air-openings 134, 136 to permit entry of anincreased volume of air to enter the mixing tube 132.

FIGS. 20-22 show various views of spring bar 148. Spring bar 148 is an“L” shaped bracket having a spring bar hole 170 for fastening the springbar to a spring plate (see 150 in FIG. 19, for example).

FIGS. 23 and 24 show a bi-metal coil spring 144 according to anembodiment of the invention. It should be noted that upper and lowerbi-metal springs 144, 146 (See FIG. 4, for example) are identical inmaterial composition and geometric configuration in this example. Forthe fireplace used in the above example, it is desired to construct thebi-metal coil springs 144, 146 from a material that withstands 1000degrees F. maximum temperature and about 800 degrees nominaltemperature. The spring type is an ASTM-TM-1, available from AtlantaAlloy Inc., and of a composite construction consisting of two or morematerials with different thermal expansion coefficients, and whichcauses the spring to unwind when heated. Other bi-metal springs or theequivalent may be used. It should be understood that the amount ofmovement of the spring and, in some embodiments, the attached shutterassembly, will correspond to the bi-metal materials used, theconstruction of the spring, and the temperature range experienced by thespring. In other words, a spring used in the mechanism of the inventionmay be lighter in construction or more sensitive to temperature changeswhen a relatively lower range of temperature is experienced and aheavier or less sensitive spring will be used when relatively higherrange of temperature change is experienced by the spring. In thismanner, a properly controlled airflow and mixing ratio is maintainedwhen applying the principles described herein to different unitconditions.

The coil springs 144, 146 are provided in the coiled configuration, inpart to be compact and usable in a small space, and in part to provide alarge amount of movement, or deflection for the temperature changesexperienced by the springs. Each of the bi-metal coil springs 144include a mounting portion 178 for attaching to the spring receiving tab154 of a spring plate 150 (see FIG. 15, for example) and spring bar 148.The attachment method is preferably welding to provide the correctpositional relationship for proper sealing of the shutter collarassembly 142 to a respective upper and lower air opening 134, 136 (FIG.4, for example). Other attachment methods may be employed, such asfasteners, screws, rivets and so on. At an end opposite the mountingportion 178 is an attachment portion 180 for attaching the bi-metal coilspring 144 to a shutter collar assembly 142 (see FIG. 4, for example andFIG. 25).

FIG. 25 shows an expanded view of one half of a shutter collar assembly142. The assembly 142 shown includes a shutter collar 172, which is acurved metallic semi-circular member. Attached to an inside surface 174of the shutter collar is a shutter gasket 176. The shutter gasket 176 ispreferably a closed cell silicone sponge gasket of medium density.

While endeavoring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicants claim protection in respectof any patentable feature or combination of features hereinbeforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon. While the apparatus and method hereindisclosed forms a preferred embodiment of this invention, this inventionis not limited to that specific apparatus and method, and changes can bemade therein without departing from the scope of this invention, whichis defined in the appended claims.

Therefore, the foregoing is considered as illustrative only of theprinciples of the invention. Further, since numerous modifications andchanges will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction and operationshown and described, and accordingly, all suitable modifications andequivalents may be resorted to, falling within the scope of theinvention.

1. A gas heating unit, comprising: a combustion chamber; and a burnerhousing assembly positioned to provide combustion to said combustionchamber, wherein said burner housing assembly includes a burner housingand a gas and air mixing assembly in communication with said burnerhousing, said gas and air mixing assembly functioning to mix gas and airto provide a yellow appearing flame instantaneously after initiation ofcombustion.
 2. The gas heating unit of claim 1, wherein said gas and airmixing assembly is automatically responsive to changes in temperature tomaintain said yellow appearing flame over time.
 3. A gas heating unit,comprising: a combustion chamber; and a burner housing assemblypositioned to provide combustion to said combustion chamber, whereinsaid burner housing assembly includes a burner housing and a gas and airmixing assembly in communication with said burner housing; said gas andair mixing assembly including a mixing tube assembly, said mixing tubeassembly including a mixing tube having at least one air opening formedat an outer end thereof and a shutter collar assembly sized, shaped andpositioned to seal with said at least one air opening of said mixingtube, said shutter collar assembly being attached to a bi-metal coilspring, said bi-metal coil spring being responsive to changes intemperature to withdraw said shutter collar assembly from said at leastone air opening in response to an increase of temperature from anambient temperature and permitting air to enter said at least one airopening.
 4. The gas heating unit of claim 3, wherein said burner housingincludes a burner housing opening sized and shaped to receive saidmixing tube.
 5. The gas heating unit of claim 3, wherein said at leastone air opening includes an upper air opening and a lower air opening.6. The gas heating unit of claim 5, wherein said shutter collar assemblyincludes a first shutter collar having a first shutter collar insidesurface and a first shutter gasket attached to said first shutter collarinside surface.
 7. The gas heating unit of claim 6, wherein said shuttercollar assembly includes a second shutter collar having a second shuttercollar inside surface and a second shutter gasket attached to saidsecond shutter collar inside surface.
 8. The gas heating unit of claim7, wherein said upper air opening includes a first shutter collarsubassembly and said lower air opening includes a second shutter collarsubassembly.
 9. The gas heating unit of claim 8, wherein said firstshutter collar subassembly is attached to an upper bi-metal coil springand said second shutter collar subassembly is attached to a lowerbi-metal coil spring.
 10. A burner housing assembly for use in a heatingunit, comprising: a burner housing and a gas and air mixing assembly incommunication with said burner housing; said gas and air mixing assemblyincluding a mixing tube assembly, said the mixing tube assemblyincluding a mixing tube having at least one air opening formed at anouter end thereof and a shutter collar assembly sized, shaped andpositioned to seal with said at least one air opening of said mixingtube, said shutter collar assembly being attached to a bi-metal coilspring, said bi-metal coil spring being responsive to changes intemperature to withdraw said shutter collar assembly from said at leastone air opening in response to an increase of temperature from anambient temperature and permitting air to enter said at least one airopening.
 11. The burner housing assembly of claim 10, wherein saidburner housing includes a burner housing opening sized and shaped toreceive said mixing tube.
 12. The burner housing assembly of claim 10,wherein said at least one air opening includes an upper air opening anda lower air opening.
 13. The burner housing assembly of claim 12,wherein said shutter collar assembly includes a first shutter collarhaving a first shutter collar inside surface and a first shutter gasketattached to said first shutter collar inside surface.
 14. The burnerhousing assembly of claim 13, wherein said shutter collar assemblyincludes a second shutter collar having a second shutter collar insidesurface and a second shutter gasket attached to said second shuttercollar inside surface.
 15. The burner housing assembly of claim 14,wherein said upper air opening includes a first shutter collarsubassembly and said lower air opening includes a second shutter collarsubassembly.
 16. The burner housing assembly of claim 15, wherein saidfirst shutter collar subassembly is attached to an upper bi-metal coilspring and said second shutter collar subassembly is attached to a lowerbi-metal coil spring.
 17. The burner housing assembly of claim 16,further including a spring plate connected to said mixing tube, saidspring plate having a pair of spring tabs extending therefrom, each ofsaid pair of spring tabs positioned adjacent a respective one of saidupper air opening and said lower air opening.
 18. The burner housingassembly of claim 17, wherein said upper bi-metal coil spring isattached to an upper of said pair of spring tabs at a mounting portionthereof and said lower bi-metal coil spring is attached to a lower ofsaid pair of spring tabs at a mounting portion thereof.
 19. The burnerhousing assembly of claim 18, when said upper bi-metal coil spring isattached to a first shutter collar subassembly at an attachment portionthereof and said lower bi-metal coil spring is attached to a lowershutter collar subassembly at an attachment portion thereof.
 20. Amethod of controlling the color of a flame in a heating unit,comprising; supplying a burner housing of the heating unit with a flowof gaseous fuel; sensing an initial start up condition of the heatingunit; limiting the amount of air flow into the burner housing of theheating unit in response to said sensing of the initial start upcondition to generate an instantaneous yellow appearing flame uponcombustion; sensing an increase of temperature relative to the initialstart up condition; and increasing air flow into the burner housing inresponse to said sensing an increase in temperature to maintain thecolor of the flame.